Table 3. Multivariable exponential AFT model with shared gamma frailty for the identification of predictors of time to next attack (inter-attack interval).

	Independent variables		Adjusted time ratio (95% CI)	p-value
	Cumulative number of attacks		1.31 (1.02-1.67)	0.035
	Disease duration		1.00 (0.99-1.00)	0.443
	Age at the most recent attack		0.99 (0.97-1.01)	0.277
	Recent attack at the optic nerve		0.64 (0.39-1.04)	0.073
	AZA and Pd, combined Tx	AZA with <6 Mo Pd	0.73 (0.23-2.3)	0.590
		AZA with ≥6 Mo Pd a	5.70 (0.69-46.77)	0.105
		AZA with continued Pd	5.34 (1.57-18.13)	0.007
	Rituximab		4.26 (1.09-16.61)	0.037
	Interferon beta		0.69 (0.35-1.35)	0.281

Abbreviations: AFT, accelerated failure time; AZA, azathioprine; CI, confidence interval; Mo, month; Tx, treatment

^a Oral prednisolone was discontinued before the next attack